The invention relates to a volume sensing device for approximately determining the volume of liquid present in, for example, a plastic disposable pipette. A large variety of pipetting operations find many applications in medicine and industry. For example, pipetting operations are used in various medical and chemical testing and analyzing procedures during which the volume of liquid present in a pipette or probe tip used in the pipetting operation needs to be closely monitored. Such a multiple pipetting operation can, for example, be carried out by a device such as described in the co-assigned U.S. Pat. Nos. 5,055,263 and 5,036,510 entitled AUTOMATED PIPETTING SYSTEM (hereinafter the "Meltzer Robot") and a device of the type disclosed in U.S. Pat. No. 4,979,093.
The volume sensing device of this invention has as one of its objects to verify the approximate volume present in the pipette tip during the pipetting operation and, if such volume deviates from a preset value, the volume sensing device emits a signal which can be detected by the data storage device of a computer connected to the volume sensing device. The signal emitted by the volume sensing device may also trigger the energizing of an alarm, such as an alarm light, for example an LED mounted in the volume sensing device.
Pipetting devices of the state of the art frequently malfunction. For example, worn syringes, leaky connections and defective disposable pipette tips or probe tips may cause malfunctioning. Also, in case blood is the liquid which is being aspirated or dispensed, clotting or coagulation of the blood may occur in the pipette tip which causes a malfunctioning of the Automated Pipetting System